Implement other smoothers including Savitzky Golay algo

[thomasms]

The Savitzky Golay filter/smoother works well for gamma spec and it would be good to have this added to the types of smoothers.
It is implemented in scipy and something similar would be great.
https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.savgol_filter.html#scipy.signal.savgol_filter